The invention relates to compositions of matter. In particular, the invention relates to compositions of matter that are usable for the repair of turbines and their components.
Turbines, airfoils, vanes, buckets, blades, nozzles, and like elements and their components (hereinafter xe2x80x9cturbine componentsxe2x80x9d), are used in high pressure applications.
Turbine components are often formed from superalloy materials. Superalloy materials possess desirable oxidation and corrosion resistance, resistance to thermal fatigue cracking, and high strength. One known superalloy material is GTD111 (a nickel-based superalloy having a composition in approximate weight percent comprising 14% chromium (Cr), 9.5% cobalt (Co), 3.8% tungsten (W), 1.5% molybdenum (Mo), 4.9% titanium (Ti), 3.0% aluminum (Al), 0.1% carbon (C), 0.01% boron (B), 2.8% tantalum (Ta), and a balance (BAL) of nickel (Ni)). The GTD111 material, when used in turbine components, is provided with one of an equiaxed (EA), single crystal, and directionally solidified (DS) microstructure.
Turbine components suffer damage and degradation during service such as often occurs at a turbine bucket""s tip. This degradation includes serious material loss at a trailing edge of the tip. The material loss is due, at least in part, to oxidation and hot corrosion damage, as well as thermal fatigue cracking of the material.
A damaged turbine component must be repaired if it is to return to service. In the past, a damaged turbine component, for example a turbine bucket with a damaged tip, has had the tip ground away to a depth approximately equal to a turbine bucket tip cover plane. A new turbine bucket tip is built up on the cover plane by a multiple weld-pass repair process, in which the repair material is fed into the weld pool as the pool is moved around the perimeter of a cover tip on the turbine component and melted thereon to form a new tip.
One such turbine component weld repair process comprises repairing by welding without both pre-heating of the turbine component and continued heating of the turbine component during the repair process. The repair material for such a turbine component weld repair process often uses a nickel-based superalloy repair material, especially if the turbine component is formed from a nickel-based superalloy material. For example, one nickel-based superalloy repair material comprises IN625 (a nickel-based superalloy having a composition in approximate atomic percent comprising 24.64% chromium (Cr), 5.6% molybdenum (Mo), 0.25% titanium (Ti), 0.44% aluminum (Al), 0.25% carbon (C), 2.1% iron (Fe), 2.3% niobium (Nb) and a balance (BAL) of nickel (Ni)). IN625 nickel-based superalloy possesses acceptable weld adherence and mechanical compatibility with a superalloy turbine material, such as a GTD111 nickel-based superalloy. Welds comprising IN625 repair material on a turbine component, such as a GTD111 turbine component, exhibit a low cracking frequency following a weld repair process. Further, a repaired turbine component comprising IN625 repair material exhibits low cracking frequency after subsequent heat treatments, which is a desirable turbine component characteristic.
An IN625 repair material, while exhibiting low crack frequency, possesses undesirable strengths and oxidation resistance in a repaired turbine component and so can only be used to repair turbine components subjected to moderated temperatures and times encountered in high pressure and temperature turbine component usage. Therefore, a GTD111 repair material was investigated as a weld repair material for repairing a GTD111 turbine component. A repair process using GTD111 repair material heats the turbine component prior to, and during, the weld repair process. The turbine component temperature reaches temperatures greater than about 950xc2x0 C. during heating to avoid forming cracks in the turbine component and repair material. The cracking would require undesirable re-work of a once-repaired turbine component, and may not correct or eliminate cracking problems in the repaired turbine components, which, of course, is undesirable.
A turbine component repaired with a GTD111 produces an enhanced strength weld repair when compared to a turbine component repaired with IN625. A repaired turbine component comprising a GTD111 is more oxidation resistant than IN625, but is prone to oxidation since its oxidation resistance is only as much as the original turbine component material""s oxidation resistance. While a repaired turbine component with GTD111 exhibits enhanced oxidation resistance compared to that of a repaired turbine component with IN625, the oxidation resistance is not as high as desirable.
Accordingly, a crack and oxidation resistant repair material for repairing turbine components is needed. The repair material should not require additional heating of the turbine component for repair, because of the undesirable cracking effects associated with heating. Further, the repair material should be more oxidation resistant than known repair materials, such as, but not limited to, IN625 and GTD111, and be as strong as or stronger than IN625.
The invention overcomes the above noted deficiencies of prior repair materials.
The invention provides a composition that comprises cobalt, chromium, carbon, boron, zirconium, aluminum, at least one refractory material, and nickel that can be used to repair a superalloy article.
Also, the invention provides a repair process for a superalloy article using a repair material. The repair material comprises cobalt, chromium, carbon, boron, zirconium, aluminum, at least one refractory material, and nickel.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.